The invention relates to a hydrodynamic sliding bearing of a shaft, in particular a magnetic coupling pump, wherein the sliding bearing comprises a clamping sleeve disposed between bearing sleeves, wherein the bearing sleeves are each mounted with their bearing front side on an axial bearing.
Magnetic coupling pumps are generally known and described, for example, in DE 10 2009 022 916 A1. In this case, the pump power is transmitted from a drive shaft via a magnet-carrying rotor (outer rotor) in a contact-free manner and substantially free from slippage onto the pump-side magnet carrier (inner rotor). The inner rotor drives the pump shaft which is mounted in a sliding bearing lubricated by the conveying medium, i.e. in a hydrodynamic sliding bearing. Located between the outer rotor and the inner rotor, i.e. between the outer and the inner magnets is the split case with its cylindrical wall. The split case is connected with its flange to a pump component, for example, a casing cover and has a closed base opposite thereto. The split case, i.e. the magnetic coupling pump reliably separates the product case from the environment so that the risk of an escape of product with all the associated negative consequences can be eliminated. A magnetic coupling pump is accordingly the combination of a conventional pump hydraulics with a magnetic drive system. This system uses the attraction and repulsion forces between magnets in both coupling halves for the contact-free and slippage-free transmission of torque. The magnetic coupling pump accordingly has major advantages particularly when handling very valuable or very hazardous substances.
EP 0 814 275 B1 is concerned with a hydrodynamic sliding bearing of a magnetic coupling pump which is configured as a combined axial and radial bearing. The sliding bearing of EP 0 814 275 B1 has two bearing sleeves, two bearing bushings which are slidable on the bearing sleeves, a spacer sleeve disposed between the bearing sleeves and a spacer bushing disposed between the bearing bushings. The bearing sleeves and bushings are made of a ceramic material, where the spacer sleeve or bushing is formed from a metal. In order to create a hydrodynamic sliding bearing which should be inexpensive to manufacture and designed so that at all times sufficient lubrication by the medium to be conveyed enters into the sliding bearing, EP 0 814 275 B1 proposes that the inside diameter of the bearing sleeves is greater than the inside diameter of the spacer sleeve. EP 0 814 275 B1 discloses that the bearing sleeve is radially centred in the cold state above the L ring of the spacer sleeve. In the warm state the centring over the extension of the shaft is taken over by the bearing sleeves. It is to be seen as a disadvantage here that particles, e.g. dirt particles can collect between the shaft and the ceramic bearing sleeve so that there is a risk that the bearing sleeves could be destroyed or could disintegrate during a thermal expansion.
Accordingly hydrodynamic sliding bearings are known the components whereof are formed from different types of materials, where for example, the bearing sleeves consist of a ceramic, e.g. of a sintered silicon carbide and the clamping sleeve or the spacer sleeve consists of a metal, e.g. a stainless steel. However, the materials exhibit different properties which should be taken into account, where for example, different (thermal) coefficients of expansion should be mentioned. In this respect during thermal stressing of the metal-ceramic connection, stresses can occur where the metallic connection partners expand more than the ceramic connection partner. The thermally induced different axial expansion can be compensated by, for example, using flexible elements such as for example flat seals as thermal compensating elements. A radial centring can be accomplished, for example, by means of tolerance rings. A disadvantage with this connection however is the inadequate compressibility and permanent elasticity of the flexible materials (axial) and the tolerance rings (radial) which over time, i.e. operating time, lead to fatigue of the material. The sliding bearing is pre-stressed during mounting. As a result of the thermal expansion, there is a risk of a release of the axial tension, in particular between the impeller and the inner magnetic rotor. Even with low axial loading behind the impeller, this results in axial enlargement of the gap in the force fit between the impeller and the ceramic bearing disks. Consequently, the impeller lurches. This leads to vibrations and exceptional loads which can lead to damage of the impeller/shaft connection (e.g. vibration failure). However there is also a risk of destruction of the ceramic component if harmful stress transitions and/or stress peaks occur which, for example, is possible if the abutting front sides are canted.